The buildbot slaves use the 7.0 STD iso for this. If you'd like to contribute packages, using the buildbot system is the way to go. you can learn how to do it by reading the docunentation at http://vlcore.vectorlinux.com/buildbot/docs

After public release of 7.1 final, will the bots be using mkchroot on 7.1 STD iso, or will there be a different buildbase

The bots will use the mkchroot tool. But 7.1 does have what we call a barebones iso. This iso is noy for public release, but rather to be used as a build base for public releases. The build slaves usechroot jails based on this iso.